Both unsaturated and saturated hydrocarbon oil in the parts per million or parts per billion range, is often present in water or in other liquids which are immiscible with oil. In many cases, various contaminants, such as salt, algae, silt, phenols, emulsifying agents, radioactive materials and other contaminants may be present. It is often necessary or desirable to measure the quantity of oil present in such a mixture. For example, it may be necessary to determine the amount of oil present in water being discharged to make certain that there is insufficient oil to have any deleterious effect on the environment. Also, it is sometimes desirable to monitor a liquid stream to determine if the quantity of oil present in the stream is sufficient to economically justify recovery of the oil. In addition, radioactive oil measurement can be of significant value.
The oil with which the present invention is primarily concerned is described herein as all saturated hydrocarbon oils, and those unsaturated oils which will not react in water by intermingling of atoms. For example, the oil may be crude oil or single or multiple saturated fractions thereof ranging, for example, from asphalt to clean lower-specific gravity crude to the very difficult to measure or treat "acid sludge" and/or BS&W present in the bottom of tanks as found in petroleum production. Also, the oil may be of the type obtained from petroleum refining and contain a wide series of hydrocarbons from distillation, including, for example, the paraffin series (methane series C.sub.n H.sub.2n+n), napthene or cycloparaffin series olefins (C.sub.n H.sub.2n-2 less H atoms), ethylene and aromatic series, and where the refinery has attendant chemical plants, oils from distillate based insecticides, etcetera.
Quantitative tests for oil in water or other liquids immiscible with oil are possible. For example, testing procedures using photometrics (in certain cases only) eight-hour hexane extraction in all cases, dyes (in certain cases only), infrared scan, spectrophotometry in all cases, conductivity (until this disclosure-useable in solvent-oil only), and others are known, but will not function in all cases, such as centrifuging, fluorescence, etcetera, as listed by the U.S. Department of Commerce S-85:950/SER:4324. However, these methods are carried out in a laboratory or in oxygen tests partially "fixed" in the field to hold sample enroute to laboratory, and this requires that samples be taken by skilled technicians, (if results are to be accurate, a service noted in all certified public testing laboratories' list of their function and costs), from a field location, which is often remote, to the laboratory, for testing. The time required for transporting the test sample and the test itself may result in substantial delay of the order of days between the time the sample is taken and the time the test results are obtained. Although some of the quantitative-oil-only testing equipment is purportedly portable, this equipment requires electrical power lines and so is not portable in the sense that it can be easily manually transported from location to location without requiring any external hook-ups of any kind, or the equipment may require a support system of such high weight or bulk as to be impractical to transport.
There are several portable oil monitors which use conductivity to measure the static charges on flammable liquids of a single composition. Information on these in the United States, United Kingdom, Germany, France and other countries has been studied and the manufacturers have reported that their devices will not operate where the sample to be tested for oil includes a mixture of water and oil and may contain more than one specific hydrocarbon fluid, particularly when the sample contains suspended debris.